I. Field of the Invention
The present invention relates to a control circuit for a servo-motor D.C. holding brake.
II. Description of the Prior Art
Industrial manufacturing facilities, such as an automotive assembly plant, utilize electric servo-motors to drive some high inertia loads. For example, such electric motors are utilized to drive turrets, framing systems, and the like.
For safety reasons, these servo-motors are equipped with a "holding brake" to prevent any free motion of the system, when the servo-motor controller is disabled. Otherwise, such electric servo-motors could provide free movement of their load and potentially injure the manufacturing equipment, the manufactured item or even maintenance persons working on it.
There have been a number of previously known electric brakes for braking the electric servo-motor in the event of a power failure. Such electric brakes typically include a pair of input terminals which are connected to the power source which also powers the electric motor. Typically, a rectifier as well as a voltage reduction circuit is conventionally interposed between the power supply for the electric motor and the brake input terminals on the electric brake.
These previously known electric brakes maintain the brake in a released condition as long as the power input to the brake is greater than a preset threshold voltage, for example 5-6 volts. However, in the event of a power failure, the voltage input to the brake terminals for the electric brake falls below the preset voltage immediately thus causing the brake to activate and stop the motor.
Although these previously known electric holding brakes have proven effective for stopping the motors in the event of a power failure, in many cases, the load being moved by the electric motor is extremely massive. In these cases, the immediate braking action of the electric motor can result in extremely high torque and other stress imposed on both the motor holding brake as well as the load being moved by the motor. Such excessive forces in some cases are sufficient to not only damage, but also destroy the holding brake and/or transmission.